Obturator for caseless ammunition firearm

ABSTRACT

A firearm capable of firing ammunition of the caseless-type The firearm has a bolt carrying a firing pin and an obturator which is slidably supported by the barrel of the firearm. The obturator is provided with a radial extending wall and the pressure of the gas within the chamber, when a round of caseless ammunition is fired, forces the obturator into tight engagement with the bolt to prevent gas leakage. The obturator also has a circumferentially extending wall of relatively thin radial dimension which is forced against the barrel when the round of caseless ammunition is fired. A ratchet-and-pawl arrangement is provided connected with the obturator and as the bolt is opened and closed and rotated during these operations the obturator is rotated in one direction. The bolt has a bore containing a firing pin seal disposed about the firing pin. This seal has an end portion formed with an axially extending groove to provide inner and outer circumferentially extending lips. These lips are expanded respectively against the bore wall of the bolt and a portion of the firing pin when a cartridge is fired to prevent gas leakage. The firing pin includes a shaft of steel material having a firing tip formed of a refractory material such as a tantalum alloy.

llnited States Patent Plumer et al.

[ Feb. 29, 1972 [54] OBTURATOR FOR CASELESS AMMUNITION FIREARM General Motors Corporation, Detroit, Mich.

[73] Assignee:

[22] Filed: July 28, 1969 [2]] Appl. No.: 845,284

Primary ExaminerBenjamin A Borchelt Assistant Examiner-Stephen C. Bentley Attorney-E. W. Christen, C. R. Meland and Albert F. Duke [57] ABSTRACT A firearm capable of firing ammunition of the caseless-type The firearm has a bolt carrying a firing pin and an obturator which is slidably supported by the barrel of the firearm. The obturator is provided with a radial extending wall and the pressure of the gas within the chamber, when a round of caseless ammunition is fired, forces the obturator into tight cngagement with the bolt to prevent gas leakage. The obturator also has a circumferentially extending wall of relatively thin [52] US. radial dimension which is forcgd against the barrel when [he 89/185 round of caseless ammunition is fired. A ratchet-and-pawl ar- 51 lm. Cl ..F4ld 11/00, F41d 1 H16 rgngelilem is Provided T with Obwrator and as t e bo t is opened and c osed an rotate uring these opera- [58] Field of Search ..89/26, 27, l55z56; 4329/2, tions the obmrator is rotated in one direction The bolt has a bore containing a firing pin seal disposed about the firing pin. This seal has an end portion formed with an axially extending References Cited groove to provide inner and outer circumferentially extending lips. These lips are expanded respectively against the bore wall UNITED STATES PATENTS of the bolt and a portion of the firing pin when a cartridge is 32 7 l 885 Tyler 89/26 UX fired to prevent gas leakage. The firing pin includes a shaft of 437,330 12/1892 Seabury ..89/26 steel material having a firing tip formed of a refractory materi- 1,345,565 7/1920 Tompson 89/27 UX a] such as a tantalum alloy, 3,114,290 12/1963 Harvey et al.. ..89/26 3,354,780 l H] 967 Ramsay ..89/26 3 Claims, 3 Drawing Figures OBTURATOR FOR CASELESS AMMUNITION FIREARM The invention herein described was made in the course of work under a contract or subcontract thereunder with the Department of the Army.

This invention relates to a firearm and more particularly to a firearm which is capable of firing caseless ammunition.

Caseless ammunition is a type of ammunition that does not utilize the normal case which contains the propellant charge such as powder. In caseless ammunition the propellant charge is molded generally to a cylindrical shape and is molded to a bullet or projectile to form a complete cartridge.

In conventional ammunition, that utilizes a case, the case expands against the chamber walls when a cartridge is fired to substantially prevent gas leakage and therefore properly propel the bullet out of the barrel of the firearm. Since there is no case to perform this function, when using caseless ammunition, the firearm must be arranged to prevent gas leakage when a cartridge is fired.

It accordingly is one of the objects of this invention to provide a firearm capable of firing caseless ammunition and to provide an obturating arrangement which prevents leakage of gas when the cartridge is fired. In carrying this object forward a cylindrical obturator is provided which is fitted to a chamber formed in the barrel of the firearm. The obturator has a radially extending wall which engages the bolt of the firearm when the bolt is in a closed position to form a seal between the obturator and the bolt. The obturator is also provided with a radially extending wall which forms a pressure surface that is contacted by the expanding gas in the chamber of the firearm to force the obturator into tight engagement with the bolt to thereby prevent gas leakage when a round of ammunition is fired. This obturator, in addition, is preferably formed with a thin circumferentially extending wall which is forced radially into engagement with the barrel chamber when the round is fired to further prevent gas leakage.

Another object of this invention is to provide an obturator for a firearm which is rotated during opening and closing of the bolt to thereby cause different sealing surfaces of the bolt and obturator to become engaged as the firearm is fired. This improves the sealing function between the bolt and obturator and also provides a wiping action between the engageable sealing surfaces of these parts.

In carrying this object forward the obturator is provided with a radially extending flange which has ratchet teeth cut therein. The ratchet teeth cooperate with one or more springbiased pawls supported by the barrel and as the bolt is rotated during opening and closing of the bolt the obturator is rotated in one direction.

Still another object of this invention is to provide a firearm firing pin seal for firearms that are capable of utilizing caseless ammunition. This firing pin seal comprises an annular part fitted within a bore of the bolt having a central opening which embraces the firing pin. The end of the firing pin seal, which faces the cartridge, is provided with an annular slot which defines a pair of relatively thin circumferentially extending lips that respectively engage an internal bore of the bolt and the firing pin. When the round of ammunition is fired any gas passing into the bolt bore through the firing pin opening radially expands the lips respectively against the bolt bore and the firing pin to thereby prevent gas leakage.

Another object of this invention is to provide a method of manufacturing a firing pin for a firearm. In carrying this object forward a steel firing pin shaft is provided. The firing pin shaft is bored out at one end and a tantalum firing pin tip, having a recessed extension, is fitted within the bore of the shaft. The shaft is swaged inwardly so that the material of the shaft is driven into the recessed portion of the firing pin extension. The firing pin can then be machined to provide a finished pin that is capable of firing caseless ammunition.

In the drawings:

FIG. I is a sectional view of a part of a firearm which is capable of firing caseless ammunition and which illustrates the obturator and firing pin seal of this invention; and

FIGS. 2 and 3 are views, partly in section, illustrating the method of connecting the shaft and tip of a firing pin made in accordance with this invention.

Referring now to the drawings and more particularly to FIG. 1 the reference numeral 10 generally designates a rectangular bolt carrier for a firearm. The bolt carrier 10 is slidably supported by a body or receiver member 11. A stock and trigger grip assembly (not illustrated) are secured to the member 11. The firearm of this invention includes a barrel 12 and a barrel extension 14 which is threaded to the barrel 12. The barrel parts 12 and 14 are suitably supported by the receiver member 1 l. The body member 11 can take the form of a U-shaped support which slidably supports the bolt carrier in its reciprocating movement. The bolt carrier 10 is preferably gas operated by means which form no part of the present invention and the firearm can be of the automatic type.

The bolt carrier 10 is connected by way of a cam-and-slot arrangement to be described with a bolt generally designated by reference numeral 16 having a bore 18. The portion 20 of the bolt 16 is provided with circumferentially spaced teeth and notches which are not illustrated and in one rotated position of this bolt the teeth are aligned with slots formed in the portion 22 of the barrel extension 14. These slots are likewise not illustrated it being understood by those skilled in the art, however, that the section 22 is provided with alternate teeth and slots which permit the bolt to slide through the slots in the part 22 of the barrel extension 14 and the bolt is rotated to lock the bolt in position. This type of bolt and barrel arrangement is called an interrupted lugbolt system.

A cam follower pin 24 fits within an opening in the bolt 16 and this cam follower pin has a head 26 riding in a cam slot 28 formed in the bolt carrier 10. It therefore will be apparent that as the bolt carrier 10 is reciprocated during operation of the firearm the bolt 16 reciprocates but will also be rotated due to the provision of the cam slot 28 cooperating with the cam follower 26. The cam arrangement is such that the bolt is rotated to a position where the teeth, on the part 20 of the bolt, become aligned with the slots in the part 22 of the barrel extension so that the bolt can be retracted and projected during operation of the firearm.

The firearm has a firing pin which is generally designated by reference numeral 29. This firing pin is comprised of a rod or shaft 30 formed of steel material which is secured to a firing pin tip designated by reference numeral 32. The firing pin tip 32 is formed of a refractory material such as a tantalum alloy. The method of securing the firing pin tip to the shaft will be described hereinafter and is illustrated in FIGS. 2 and 3. It is seen that the end of the firing pin tip 32 passes through an opening 33 formed in an annular liner designated by reference numeral 34 which is press fitted into a bore 36 formed in the bolt 16. This liner is preferably formed of a tantalum alloy. The shaft section 30 of the firing pin passes through a bore formed in a cylindrical firing pin seal 39. The firing pin shaft passes through an opening formed in the bolt carrier 10 and has an end portion 40 which is struck by a hammer (not illustrated) when a round of ammunition is fired. The bolt carrier receives a firing pin retainer designated by reference numeral 42.

The firing pin seal 39 is preferably formed of a metal material such as beryllium copper and one end of this seal has an annular groove 48 providing first and second circumferentially extending lips 50 and 52. These lips have a relatively thin radial dimension as is clearly apparent from FIG. 1 and when a round of ammunition is fired any gas expanding into the chamber 54 will radially expand the lips. The lip 52 will be radially expanded into engagement with the wall forming the bore 13 while the lip 50 will be radially expanded inwardly to tightly embrace the shaft 30 of the firing pin 29. This will provide a tight seal between the firing pin seal, the bolt and the firing pin to prevent leakage of gas that may pass into the chamber 54.

The obturator of this invention is generally designated by reference numeral 60 and is formed of steel material. The obturator has a circumferentially extending flange 62 formed with ratchet teeth 64 extending around the periphery thereof. The ratchet teeth 64 are engaged by pawls 66 and 66 which are urged into engagement with the ratchet teeth by flat spring metal members 70 and 72 secured to the barrel extension 14 by screws as shown in FIG. I.

The obturator 60 has an internal bore 74 which receives a round of caseless ammunition the projectile or bullet of which is positioned in the barrel opening 12A. The obturator 60 has an outer circumferentially extending wall engaging an inner annular wall 12B formed in the barrel 12. The fit between the obturator and the wall 12B is such that the obturator can move axially and rotatably with respect to the barrel 12. The obturator 60 further includes an annular section 76 forming a radial lip of relatively small radial dimension which is expanded into contact with the wall 12B of the barrel when a cartridge is fired. The obturator further includes a radially and circumferentially extending wall 78 forming a pressure surface upon which the expanding gas impinges to force the obturator toward the bolt in FIG. 1 when a cartridge is fired. The obturator has a chamfered sealing surface 79 which engages a complementary surface formed on the bolt 16. Extending from the sealing surface 79 is a section 30 having an end wall 32 fitted within the bolt 16 when it is closed. A Belleville spring 84 is provided located between the end of the barrel I2 and flange 62 which urges the sealing face 79 against the complementary sealing face on the bolt 16 when the bolt is in a closed position.

The net effective area to be acted upon by gas pressure, defined by end walls 78 and 86 of the obturator 60, is greater than the net area defined by walls 79 and 82 and the ratio may be approximately three to one. This means that when a cartridge is fired within the chamber defined by the bolt 16 and the bore 74 of the obturator the gas pressure developed will force the obturator toward the bolt providing a tight seal between the sealing face 79 and the sealing face on the bolt 16 to prevent gas leakage.

The ratchet-and-pawl arrangement which has been described provides for rotation of the obturator 60 during opening and closing of the bolt 16. The rotational sense of the ratchet teeth 64 is such that the obturator is rotated in one direction when the bolt 16 is rotated during opening of the bolt. The rotation is due to the frictional engagement between the bolt 16 and the obturator 60 as the bolt is rotated just prior to opening of the bolt. When the bolt closes it of course is rotated in an opposite direction but the ratchet arrangement now prevents rotation of the obturator 60 as the bolt is rotated to a closed position.

The rotation of the obturator 60 has important advantages. Thus, there is a wiping action between the bolt 16 and the sealing face 79 of the obturator as the bolt is rotated to a closed position since during this direction of rotation of the bolt the pawl-and-ratchet arrangement prevents rotation of the obturator. In addition, by continuously rotating the obturator during firing of the firearm any leaks that may develop on the sealing surface are more effectively blocked because they occur at different circumferential points on the bolt face each time the bolt is opened and closed and spot erosion of the bolt face is therefore reduced.

Referring now more particularly to FIGS. 2 and 3, a method of fabricating the firing pin for the firearm of this invention is illustrated. In fabricating this firing pin a rod or shaft of steel material 28 is provided which has a larger diameter end section 28A. The steel rod is bored out to form the bore 283 shown in FIG. 2. A firing pin tip 32 is then provided which is formed of a refractory material such as a tantalum alloy. This firing pin tip 32 has an axially extending section 32A which is formed to provide the groove 328. The extension 32A is slipped into the bore 288 of the steel shaft until wall 32C engages wall 28C. The section 28A is then swaged inwardly so that the steel material of the shaft fills the slot 328 as shown in FIG. 3. The tantalum tip 32 is now securely fastened to the steel rod or shaft 28 and the steel shaft is then machined to provide the finished firing pin shown in FIG. 3.

It Wlll now be appreciated that an obturator has been provided which can both rotate and move axially relative to the barrel during firing of the firearm. This provides, in effect, a floating obturator which is moved axially against the bolt when a cartridge is fired by differential forces due to gas pressure acting on the pressure surfaces of different effective areas located on opposite ends of the barrel supported obturator.

It is pointed out that the pawls 66 and 68 have portions 66A and 66B which engage an end of the obturator and serve to retain the obturator 60 against axial movement out of the barrel 112 under the force of Belleville spring 84 when the bolt is in an open position. It is also pointed out that the frictional engagement of the lip 86 and the barrel bore 128, when a cartridge is fired to force lip 86 radially outwardly, is not sufficient to prevent the obturator 60 from being moved axially to provide tight engagement between the sealing surface 79 on the obturator and the complementary surface on the bolt.

What is claimed is:

1. An obturating arrangement for a firearm comprising, a barrel for said firearm, a reciprocable and rotatable bolt, a bore in said barrel, an obturator having an internal bore and an external surface engaging the bore wall of said barrel whereby said obturator can rotate relative to said barrel and is supported thereby, sealing surfaces disposed respectively on said obturator and said bolt which are engaged when said bolt is moved to a closed position, the internal wall of said bolt and the internal wall of said obturator fonning a firing chamber for a cartridge, and ratchet-and-pawl means connected with said obturator permitting rotation of said obturator in one direction but preventing rotation of said obturator in an opposite direction, said obturator being rotated in said one direction by frictional engagement between said bolt and obturator as said bolt is rotated in one direction, said bolt sliding relative to said obturator when said bolt is rotated in said opposite direction to provide a wiping action between the sealing surfaces on said bolt and obturator.

2. The firearm according to claim 1 where the ratchet-andpawl means comprises ratchet teeth disposed upon a radially extending flange of the obturator and where at least one pawl is spring biased axially into engagement with the ratchet teeth and is fixed relative to the barrel.

3. The obturating arrangement according to claim I where the ratchet-and-pawl means comprises ratchet teeth formed on the obturator and at least one spring-biased pawl carried by the barrel and engaging the teeth, the pawl having a means engaging the obturator for preventing axial movement of the obturator out of the barrel under the influence of a loading spring located between the barrel and obturator. 

1. An obturating arrangement for a firearm comprIsing, a barrel for said firearm, a reciprocable and rotatable bolt, a bore in said barrel, an obturator having an internal bore and an external surface engaging the bore wall of said barrel whereby said obturator can rotate relative to said barrel and is supported thereby, sealing surfaces disposed respectively on said obturator and said bolt which are engaged when said bolt is moved to a closed position, the internal wall of said bolt and the internal wall of said obturator forming a firing chamber for a cartridge, and ratchet-and-pawl means connected with said obturator permitting rotation of said obturator in one direction but preventing rotation of said obturator in an opposite direction, said obturator being rotated in said one direction by frictional engagement between said bolt and obturator as said bolt is rotated in one direction, said bolt sliding relative to said obturator when said bolt is rotated in said opposite direction to provide a wiping action between the sealing surfaces on said bolt and obturator.
 2. The firearm according to claim 1 where the ratchet-and-pawl means comprises ratchet teeth disposed upon a radially extending flange of the obturator and where at least one pawl is spring biased axially into engagement with the ratchet teeth and is fixed relative to the barrel.
 3. The obturating arrangement according to claim 1 where the ratchet-and-pawl means comprises ratchet teeth formed on the obturator and at least one spring-biased pawl carried by the barrel and engaging the teeth, the pawl having a means engaging the obturator for preventing axial movement of the obturator out of the barrel under the influence of a loading spring located between the barrel and obturator. 